Liquid containment tanks or containers are used in a number of industrial processes such as food manufacturing, pharmaceutical manufacturing, chemical processing, material fermentation and so on. It is often critical to ensure that the interior of the tank is free of unwanted debris and contaminants. For example, a tank that is typically filled to a certain level may exhibit a “tub ring” about its interior circumference at the level to which the tank is most often filled. Also, various equipment within a tank, tank inlets and outlets etc. may trap sediment or debris that may later reenter the tank contents during use.
Unwanted contaminants in the tank may negatively influence the quality of the finished product being manufactured, processed or stored in the tank. Also, the interior of a tank must be properly cleaned if regulations applying to certain industries such as pharmaceutical industries shall be followed. Thus, it is common to clean the interior of such tanks at certain intervals, e.g. after each process batch, to ensure product quality and adherence to any relevant regulations.
Tank cleaning systems are available that clean debris and residue from the interior of tanks and other vessels through the use of what is commonly known as impingement cleaning. One common type of such systems employs a cleaning apparatus that is inserted into the tank and which has a hose or pipe that extends into the tank. At an end of the pipe protruding into the tank, a rotary jet head is affixed. The rotary jet head is commonly rotatable about one or two axes and, in the latter case, is typically geared such that as the jet head rotates about an axis of the pipe, it also turns upon an axis perpendicular to the pipe.
A relationship between rotations about two axes depends on a gearing ratio, which is selected such that a combination of a particular orientation and position of the jet head repeats only after multiple revolutions around the axis of the pipe. This technique staggers subsequent traces of the spray against a tank interior on each revolution of the rotary head to ensure that substantially every portion of the tank interior is exposed to the cleaning spray at some time during the cleaning process. The accomplished traces of the spray against the tank provide a cleaning apparatus that sprays cleaning liquid in a predetermined pattern on the interior surface of the tank.
In order to ensure that the interior of a tank is adequately cleaned the cleaning liquid should be sprayed in a predetermined pattern. Alternatively, a cleaning duration may be prolonged, which however may lead to excessive waste of time, cleaning fluid, and energy.
A tank cleaning apparatus is commonly a fixed installation in the sense that it is seldom or even never removed from the tank in which it is installed. This means that also the tank cleaning apparatus itself preferably shall be cleaned during a cleaning process in order to not complicate the cleaning process by e.g, requiring a separate subsequent cleaning of the cleaning apparatus. An unsatisfactory cleaned cleaning apparatus may result in that debris and residues are remaining on the cleaning apparatus after a completed cleaning process. Such remaining debris and residues may later on reenter contents of the tank resulting in that the contents may become negatively affected or contaminated.
To ensure an adequate cleaning of the tank and the cleaning apparatus different techniques have been suggested and employed. For example, patent document US 2012/0017951 A1 discloses a tank cleaning system utilizing nozzles to provide flush liquid streams on an interior surface of an enclosed space, like a tank. One or more of the nozzles used are arranged in an angled fashion such that the flush liquid streams from the angled nozzles impinge on the liquid pipe, on which the cleaning apparatus is mounted, to some extent thereby providing a cleaning effect to the liquid pipe. Patent document, WO 2014/072087 A1, on the other hand, discloses how cleaning is improved by employing nozzles having a dual spray pattern, resulting in that the interior of the tank is cleaned as well as the fluid line on which the cleaning apparatus is mounted. This is achieved by the dual spray pattern which is designed such that both the interior of the tank and the liquid pipe, on which the cleaning apparatus is mounted, is sprayed to some extent.
The cleaning apparatus may also be used for mixing a content of the tank. This is typically done by filling the tank with the content until the rotary jet head is fully underneath a surface of the content. The content is then mixed by circulating it from an outlet of the tank and back into the tank via the rotary jet head. As with cleaning, mixing must be adequately performed and it is important that this may be done without e.g. excessive circulation of content. When a tank cleaning apparatus is capable of also performing mixing of a content of the tank, the apparatus is often referred to as a liquid ejection apparatus rather than a cleaning apparatus.
Present techniques provide solutions for cleaning of the interior of tanks and mixing of contents of a tank. Moreover, present techniques provide solutions for cleaning the pipe or liquid line onto which the cleaning apparatus or liquid ejection apparatus is mounted. However, in some cases the cleaning of the cleaning apparatus itself has proven to be non satisfactory, resulting in that debris or residues remain on the cleaning apparatus even after a completed cleaning process. If debris or residues remain on the cleaning apparatus after a cleaning process, this may result in that the contents of the tank are negatively affected or contaminated during subsequent use of the tank.
Hence, there is a need for an improved liquid ejection apparatus.